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192                      GANODONTA--CALAMODON                     CHAP.
but reduced by one premolar at least in the upper jaw. It is very
important to notice that the incisors have enamel only on their
anterior faces, and that the same is the case with the canines,
the slender layer present behind the tooth in Hemiganus having
vanished in this later form. The tooth pattern of the molars is
like that of Semiganus. The fore-limb is decidedly Edentate-
like; but it is the foot which presents the strongest likenesses to
that order. " If an anatomist/' remarks Dr. "Wortnian, " had no
other part of the skeleton than that of the foot to guide his judg-
ment, and he should fail to detect a most striking similarity
between it and that of the Edentata, especially the Ground Sloths,
he would not only lay himself open to the criticism of being
lacking in the ordinary powers of observation and comparison, "but
would be suspected of placing the matter upon a basis other than
that established by sucK a method." It is not certain how many
toes upon the fore-limbs were possessed by Psittacotherium, but
the close resemblance to Mylodon is indeed striking, the third
digit being in both forms the most pronounced. Some vertebrae
of this G-anodont have been discovered which do not show the
complex articular arrangements of later American Edentates. The
sacrum, on the other hand, is very like that of the Sloth, and there
is a foreshadowing of the attachment of the ilia to the sacrum by
co-ossification which is met with in later Edentates. A still later
type is the genus Calccmodon, which has been shown to occur in
Europe as well as in America. C. si?nplex was a larger beast
than either of the genera that have already been treated of, thus
affording another example of the increase in size of later as com-
pared with earlier members of the same group, so pronounced
among the Ungulata. The lower jaw has the same massive
structure that characterises that bone in Hemiganus and Psitta-
cofherium. There is but one incisor, but the premolar and molar
series are complete. The canine is Rodent-like in appearance,
being imbedded throughout the greater part of the lower jaw ; it
evidently grew from a persistent pulp. It is enamelled upon the
anterior face only. The premolar and molar teeth are in this
genus commencing to lose their enamel, which is distributed in the
form of vertical bands, leaving interspaces which are not covered
by enamel. These teeth, moreover, are decidedly hypselodont,
more decidedly so than in Psittacotherium; they are, when unworn,
quadrlciispidate, with accessory cusps j when more worn, the teeth